1. Field of Invention
The present invention relates to a processes for preparing 2,3,3,3-tetrafluoropropane (1234yf).
2. Related Art
Chlorine-containing compounds, such as chlorofluorocarbons (CFCs), have been employed as refrigerants, foam blowing agents, cleaning agents, solvents, heat transfer media, sterilants, aerosol propellants, dielectrics, fire extinguishing agents, and power cycle working fluids. Such chlorine-containing compounds have proven to be detrimental to the Earth's ozone layer. Many of the hydrofluorocarbons (HFCs), used as the substitutes of CFCs, have been found to contribute to global warming. For these reasons, there is a worldwide effort to develop new compounds that are more environmentally benign while at the same time being as effective, or more effective, from a performance standpoint.
Compositions containing fluorinated olefins, including particularly 2,3,3,3-tetrafluoropropene (1234yf), are among the materials being developed for use in the aforementioned applications. In addition, 2,3,3,3-tetrafluoropropene (1234yf) can be used as feedstock monomer for synthesis of fluoropolymers and macromolecular compounds.
Methods for the production of 1234yf are known. For example, U.S. Pat. No. 7,560,602, which is assigned to the assignee of the present invention and which is incorporated herein by reference, discloses a process for producing 2,3,3,3-tetrafluoropropene (1234yf) by catalytic dehydrofluorination of 1,1,1,2,3-pentafluoropropane (245eb). While this patent discloses a process having relatively high conversion and selectivity levels, and is therefore desirable and effective from the standpoint, applicants have nevertheless come to appreciate that several disadvantages are associated with processes of the type disclosed in this and similar patents. For example, the process disclosed in Example of 6 of this patent produces approximately three percent by weight of components that are described as being unknown. Applicants have come to appreciate that these byproducts can have a detrimental impact when used in connection with one or more of the applications mentioned above.
Applicants have also come to appreciate the presence of such undesireable materials in 2,3,3,3-tetrafluoropropene (1234yf) product can result, in at least certain cases, from the presence in the 1,1,1,2,3-pentafluoropropane (245eb) feedstock of certain impurities. More particularly, applicants have come to also appreciate that certain materials available as a source of 245eb include other components that contribute, when used as feed stock source for the production of 1234yf, to a reaction product composition containing high levels of contaminants, including trifluoropropene and 1,2,3,3,3-pentafluoropropene (1225ye). Applicants have come to appreciate that these and other materials can have a negative impact on the resulting product. For example, the aforementioned materials are undesirable in the 1234yf product because of their undesirably high level of toxicity.
Applicants have found, especially in view of the deficiencies noted above, improved processes for the production of 1234yf.